1. Field of the Invention
The present invention relates to an Ni—Cu—Zn-based ferrite material and a process for the production thereof, and particularly to an improvement in relative resistance and Q value of the ferrite material.
2. Description of the Prior Art
With the popularization of portable devices, miniaturization of electronic devices is rapidly being promoted. A demand of further miniaturization of parts, such as laminated chip inductors, used for electronic devices is increasingly growing. A laminated chip inductor has a structure comprising a laminate of alternating magnetic ferrite layers and internal electrodes, and an external electrode electrically connected to the internal electrodes. In order to attain the small height of a laminated chip inductor, it is necessary for a magnetic ferrite layer to be made thinner. This requires the magnetic ferrite layer to have high relative resistance.
In not only laminated chip inductors, but also coiled inductors, ferrite material is required to be highly resistive. Surface-mounted type parts, such as laminated chip inductors and coiled inductors, manifest high reliability when being highly resistive. A ferrite material high in relative resistance is low in eddy electric loss and high in Q value and, therefore, development of a ferrite material high in relative resistance is highly desired in order to obtain a ferrite material having a high Q value.
To fulfill this desire, as a magnetic oxide, that high in relative resistance has to be used. Ni—Zn-based and Ni—Cu—Zn-based ferrite materials, for example, have been used because the relative resistance thereof is higher in order of magnitude than that of Mn—Zn-based ferrite material. When considering further miniaturization and reliability of laminated chip inductors and further reliability of coiled inductors, the relative resistance of Ni—Zn-based and Ni—Cu—Zn-based ferrite material has to be further enhanced.
As techniques of making Ni—Zn-based ferrite material highly resistive, there can be cited JP-A 2000-233967, Japanese Patent No. 3275466, JP-A 2000-150221, JP-A 2001-44016, JP-A 2002-141215 and JP-A 2002-255637, for example. JP-A 2000-233967 discloses a process of the production of a ferrite sinter having a magnetic permeability and a Q value enhanced with the addition of B4C and further discloses the addition of Mn2O3 to materialize a higher magnetic permeability and a higher Q value, heighten the relative resistance and prevent the insulation resistance from being lowered. In Japanese Patent No. 3275466, laminated chip parts high in strength and excellent in insulation resistance are disclosed, with an Ni—Cu—Zn-based ferrite material containing zirconium oxide as a magnetic substance. In addition, JP-A 2000-150221 discloses a low loss magnetic oxide material comprising an Ni—Zn ferrite material containing Sb2O5. Furthermore, JP-A 2001-44016 discloses an Ni—Zn-based ferrite material containing oxides of Bi and V. In these prior art references, addition of these oxides enables the high resistance of the Ni—Zn-based materials to be realized. JP-A 2002-141215 discloses an oxide magnetic material excellent in high frequency performance and high in volume resistance rate with the addition of Bi2O3 and oxide having quadrivalent positive ions and having suppressed disappearance of an internal conductor owing to diffusion of Ag that can be sintered through low temperature calcination. Moreover, disclosed in JP-A 2002-255637 is a highly relative resistant, magnetic oxide, porcelain composition having Sn, Co and Bi oxides contained in an Ni—Zn-based ferrite material.
Generally, the relative resistance is directly proportional to the sintering density, in view of which the aforementioned prior art references make attempts to add an oxide having a low melting point, such as Bi2O3, Sb2O5 or V2O5, or glass having a low melting point in order to make the relative resistance higher. However, the addition of such oxide of low melting point and such glass of low melting point is liable to induce extraordinary growth of particles in a sintered body and deterioration of magnetic characteristics thereof. These are problematic problems.
The present invention has been accomplished in consideration of the problems conventionally encountered and has as an object to provide an Ni—Cu—Zn-based ferrite material of high characteristics particularly having high relative resistance and to provide a process for the production thereof.
In order to attain the above object, the present inventors have been making keen studies repeatedly over a long period of time. As a result, they have found that the addition of TiO2 enables the relative resistance to be remarkably improved, i.e. to be one-order higher or more. The present invention has been accomplished based on this knowledge.